1. Field of Invention
The present invention pertains to the field of optical systems. More particularly, this invention relates to an optical homogenizer.
2. Art Background
An optical system commonly includes a photon detector which generates an electrical signal in response to photons emitted from a light source. An example of a photon detector is a photo multiplier tube (PMT). A PMT includes a photo-cathode element which emits electrons in response to photons which strike it. A PMT also includes elements for multiplying, i.e. amplifying, the emitted electrons. The output of a typical PMT is an electrical signal that indicates the number of photons that strike its photo-cathode element which in turn indicates the brightness of a light source.
A photon detector is commonly characterized by its quantum efficiency. For example, the quantum efficiency of a PMT indicates the percentage of incident photons that cause photo-electric emission from its photo-cathode element. It is usually desirable to employ a photon detector with a high quantum efficiency. A high quantum efficiency usually yields a more sensitive photon detector because the sensitivity of a photon detector is a product of its quantum efficiency and its gain. A high sensitivity usually yields a higher signal to noise ratio in an optical system. In systems in which signal-to-noise ratio is limited by the Poissonian statistics of photons or photo-electrons, the signal to noise ratio may be improved by a higher quantum efficiency buy not by higher gain.
One type of photon detector known to have a relatively high quantum efficiency is referred to as a side-on PMT. A typical side-on PMT though providing relatively high quantum efficiency also has a non-uniform response along the length of its photo-cathode element. As a consequence, the sensitivity of a side-on PMT usually varies depending upon which area of its photo-cathode element is illuminated. Unfortunately, such a non-uniform response can make light sources of equal brightness appear to have differing brightness. This can cause errors in, for example, an imaging system in which light emanating from an image is scanned into a side-on PMT.